1. Field of the Invention
The invention relates to a heat exchanger of the type comprising a corrugated metal sheet in close contact with tube sections. The invention further relates to a method and an apparatus for manufacturing such a heat exchanger.
2. Description of the Related Art
A corrugated sheet includes a first side having a plurality of first troughs alternating with a plurality of first peaks, and a second side having a plurality of second troughs alternating with a plurality of second peaks. Each trough is formed by a pair of walls, each wall separating the first side from the second side and extending from a first peak to a second peak, the troughs and peaks extending in parallel and defining a longitudinal direction.
Heat exchangers utilizing a corrugated metal sheet in close contact with cooling tube sections are well known. The cooling tube sections are typically soldered to the peaks of the corrugated sheet transversely to the longitudinal direction, as disclosed by U.S. Pat. Nos. 5,564,497 and 6,035,927. It is also known to punch elongate apertures into the sheet prior to corrugating in order to form transverse channels in the peaks for receiving the tube sections, as disclosed in U.S. Pat. No. 4,778,004, and to punch holes in the sheet to provide passages through the walls for the tube sections. While the tube sections typically carry a heat transfer fluid from an object to be cooled, it is also possible that the tube sections are phase change devices known as heat pipes, or even solid metal which simply conducts heat without the use of a heat transfer fluid. The guiding principle in each case is the establishment of close contact between the tube sections and the corrugated metal sheet which dissipates heat from the tube sections.
The prior art suffers from the disadvantage that the contact area between the tube sections and the corrugated sheet is very limited. For example, the tube sections in U.S. Pat. No. 6,035,927 have only point contact with the peaks of the corrugated sheet. The tube sections in U.S. Pat. No. 5,564,497 are formed flat, so that the thermal contact with the peaks is a essentially a line contact. Both of these structures rely heavily on solder to enlarge the path of thermal conduction. Heat exchangers having channels or holes in the corrugations improve the contact area, which is still usually enhanced by solder, but the sheet must be precisely aligned during corrugating, so that the channels or holes are precisely aligned for receiving the tube sections. This adds to the cost of manufacture.
The object of the invention is to establish heat conducting contact over a large area between the corrugated sheet and the tube sections, without the necessity of providing apertures in the sheet in order to provide channels or holes to accommodate the tube sections in the corrugated sheet, and without the provision of specially shaped tube sections.
According to the invention, this object is achieved by forming each first peak with at least one depression, the depressions in respective peaks being aligned to form at least one tube-receiving channel extending transversely to the longitudinal direction of the peaks and troughs. The channels are typically straight (rectilinear), but may be curved or otherwise routed to accommodate tubing which is formed to maximize heat transfer in a desired area of the corrugated sheet, as may be dictated by the location of components to be cooled. Each depression has a contact surface formed in the first side and extending laterally over each adjacent first trough, the contact surface being profiled to conform closely to a tube section received thereagainst. The contact surface profile is circular when standard round tubing is used, but may be formed to accommodate tubing having other shapes. For example, tubing having an oval cross-section may be used to minimize resistance to airflow by the parts of the tubing sections which stand proud of the peaks. The tube sections can thus be received in the tube-receiving channels with an area of thermal contact which is very large in comparison with the prior art, even before solder is applied. The use of solder or epoxy may therefore be minimized, which reduces the cost of manufacture. The contact surfaces also provide for easy deposition of solder for a reflow process.
The invention also relates to a method of manufacturing the heat exchanger according to the invention. The method utilizes a first fixture comprising a first base and a plurality of parallel first ribs fixed to the base, each first rib having an edge remote from the base and at least one notch extending downward from the edge, the notches being aligned to form at least one forming channel extending transversely of the first ribs. According to the method, a corrugated sheet of the type described above is placed on the first fixture so that the first ribs are received in the second troughs. A mandrel is then used to deform the first peaks downward into the notches to form the depressions which are aligned to form the at least one tube-receiving channel. The mandrel and the notches preferably have circular profiles, so that cylindrical contact surfaces are formed for receiving cylindrical tube sections. Note that the corrugated sheet may also be deformed by other apparatus and methods, such as a rolling ball or a ball end mill. The latter could be wiped across the peaks (XY motion), or could be reciprocated (Z motion) and used as a punch to form depressions in the peaks. In this regard, it is possible to form depressions by vertical movement of a spherically shaped anvil.
In order to stabilize the corrugated metal sheet while the tube-receiving channels are being formed, a second fixture is used. The second fixture includes a second base and a plurality of second ribs fixed to the second base, the second ribs and the second base being interrupted to form at least one window extending through the second fixture. The second fixture is placed onto the first fixture after the corrugated sheet is emplaced on the first fixture, and before forming the first peaks downward into the notches to form the depressions, the second ribs being received in the first troughs and the windows being aligned with the forming channels. The first peaks can then be deformed downward to form the tube-receiving channels by using at least one mandrel received through the windows in the second fixture. The second fixture stabilizes the corrugations against deformation except in the areas immediately adjacent to the notches in the first ribs, whereby peaks of the corrugated sheet are formed downward and laterally into the windows, so that the resulting contact surfaces extend laterally over the adjacent first troughs.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.